So TSW2020 has resurfaced on Steam after being delisted for quite a long time. Maybe I missed an announcement or something, but it certainly surprised me. Does DTG have the GWR license again, or could this just be related to the GWE route remaster? Either way, it's weird how TSW2020 has come back now. https://store.steampowered.com/app/530070/Train_Sim_World_2020/
Funny, after I bought a Steam Key for twice the price, although it was the Collector's Edition version, it is now available for purchase via Steam. I hope that one day these exclusive contents go on sale promotion, they are on my shopping list. https://store.steampowered.com/app/577357/Train_Sim_World_Northeast_Corridor_New_York/ https://store.steampowered.com/app/577359/Train_Sim_World_CSX_GP402_Loco_AddOn/ https://store.steampowered.com/app/1010135/Train_Sim_World_Amtrak_SW1000R_Loco_AddOn/
The GP40-2 was last on sale in February. The other two were last on sale last year. I reckon there's a small chance of them going on sale again, but I wouldn't count on it. You might be able to set up SteamDB so they send a notification if it goes on sale, but I haven't tried that out myself.
If you don't already use a watchlist manager, isthereanydeal.com is good for setting up price alerts.